Resistance to environmental stress is an important trait in crops, and has until now been thought to be a complex trait controlled by a plurality of genes called quantitative trait loci (QTLs). Identifying these QTLs is believed to be important for achieving stable crop production in the world. The inventors have previously disclosed a method of screening gramineous plants having specific traits, and gene markers for use in such a method (Patent Document 1). In the course of conducting research on the low temperature germinability in rice, the inventors have also found, through QTL analysis of genes for germinability in rice, three QTLs, qLTG-3-1, qLTG-3-2, qLTG-4, on chromosome 3 and chromosome 4. The locus qTLG-3-1 which was found at the end of the short arm of chromosome 3 has a very large activity, from which it was concluded that it might be useful for improving the low temperature germinability in rice (Non-Patent Document 1).
In addition, of the three QTLs which act on the low temperature resistance at the germination stage, the inventors have carried out fine mapping on qLTG-3-1 (Non-Patent Documents 2 and 4). As a result, they have succeeded in narrowing the candidate regions for qLTG-3-1 to the approximately 96-kb region between the marker SSR125411-4.1 and the marker STS73-28 (Non-Patent Document 2). It was possible, from the fine mapping of QTLs controlling low temperature germinability, to infer this to be a candidate region for qLTG-3-1.
The inventors have also carried out QTL analyses on the seed germinability in rice under stress. The results suggest that qLTG-3-1 participates in responses to diverse stresses, including temperature, salt (NaCl), and osmotic pressure (mannitol) stress. In this QTL analysis, it became clear that a Italica Livorno gene exhibits a germinability-increasing activity and that a QTL which exhibits a high germinability to both salt and osmotic pressure stresses exists at the end of the short arm of chromosome 3 (Non-Patent Document 3).
Thus, low temperatures are a major environmental stress in world crop production, and the inventors have hitherto found, by means of QTL analysis using Italica Livorno, which has a high low-temperature germinability, three QTLs (quantitative trait loci) which participate in low temperature germinability. However, environmental stresses had been thought to be complex traits controlled by a plurality of genes, the genetic function of the qLTG-3-1 phenotype had remained to be clarified, and the qLTG-3-1 gene had yet to be isolated, identified or cloned.                Patent Document 1: Japanese Patent Application Laid-open No. 2003-180362        Non-Patent Document 1: Ikushugaku Kenkyu 5 (Suppl. 2), p. 212 (2003)        Non-Patent Document 2: Ikushugaku Kenkyu 8 (Suppl. 1), p. 153 (2006)        Non-Patent Document 3: Ikushugaku Kenkyu 5 (Suppl. 1), p. 117 (2007)        Non-Patent Document 4: Theor. Appl. Genet., 108:794-799 (2004)        
In light of these circumstances, the inventors have reflected on the above prior art and conducted extensive investigations with the aim of elucidating the genetic function of the qLTG-3-1 phenotype, isolating and identifying the qLTG-3-1 gene, and creating transformants by cloning this gene. In the course of these investigations, to elucidate the above QTL at the molecular level, the inventors have identified qLTG-3-1 by means of chromosome map-based cloning and discovered that this gene encodes proteins of unknown function. Also, qLTG-3-1 is strongly expressed in the embryo at the time of seed germination and, in transgenic plants obtained by means of a qLTG-3-1 promoter fused to GUS, distinctive GUS staining was observed in the bud scales and ventral scales which cover the coleoptile and seminal roots. The inventors also conducted further studies, in the course of which they succeeded in elucidating the function of qLTG-3-1, determining the base sequence of the qLTG-3-1 gene, determining the amino acid sequence encoded by this gene, creating transformants with the gene, and developing techniques for utilizing the gene.